I admit to being one of the IE users up there. Reasons? OK:
-Security:
Runs in its own environment with highly restricted process permissions (IE can't even rename files without causing a UAC prompt). So far, I know no other browser using this Win7 feature.
-Resource usage:
I've been using Firefox for a long time before IE8, and quite often the program would use about 800MB of RAM for three tabs, as well as completely using both my CPU cores, thus locking itself as well as my system up almost to a full stop for a few minutes, with no apparent reason. It was probably caused by Ad scripts running amok, because IE reported a script error on the same pages, prompting me to just cancel the script.
-Stability:
Each IE tab runs in its own process. If one of them locks up, I can still use the others. If one of them crashes, I can also still use the others, while the one that crashed gets restored, including any text I entered there.
-Usability:
IE makes full use of the jumplist feature, so I can access recent pages and a few favourites really quickly. Also, IE bookmarks can be launched from within the normal Windows GUI.
-Web Slices:
Seriously, I love these things. With one click, I get a weather report, or see my Social networking news.
-Full support of Bing features:
OK, Bing seems to be a lame Google ripoff, but as long as the browser supports all of its features, Bing maps is much more comfortable and quicker than Google, and the search offers a quick preview when hovering over results, as well as dynamically loading image search results, although Google implemented these as well recently.
Also, the Bing homepage pictures are really neat.
-Automated Synchronisation of bookmarks between my desktop and my netbook without me having to do anything.
-frequent, nonintrusive updates:
When security problems arise, a fix will be available soon, and Windows downloads and installs it using a background process that doesn't require any interaction (if it's set to work on its own)
-Easy tab switching:
When I'm looking for a specific tab, I just click on the IE icon and get a list of everything open in any IE window, and can select them there. And if there aren't too many tabs open to fit on my screen, I also get a preview.
-nonintrusive prompts:
When IE wants to tell me anything (file download happening, something crashing, popup blocked, whatever) all that happens is a small yellow bar appearing at the bottom of the window, not blocking anything, and allowing all page interactions.
-nice download manager:
Finally it got one, and it's actually pretty useful. If a download breaks, it can be resumed, if you need a file again, but can't just restart the download, IE remembers the referrer page.
I think that's everything so far, but for me it's enough.
I've been using Safari for a while, but then decided that a browser should not install three additional intrusive programs with any update. After I switched from XP to Win7, thus starting with a clean system, I decided to not even download any Apple installer. After I uninstalled Quicktime, iTunes, Safari and Bonjour (actually, who needs Bonjour in times of UPnP, which is used by everything NOT made by Apple?) I kept finding folders, files and registry entries of all four all over my harddisk for weeks. Apparently Apple doesn't care for not littering on user harddisks, maybe keeping systems clean is not individual enough...
I tried Chrome once, too. It wasn't bad actually, but I still like IE better.